Liquid-cooled gaseous-discharge tube



July 24, 1956 J. H. HuTcHlNGs 2,756,027

LIQUID-COOLED GASEOUS-DISCHARGE TUBE Filed July 30, 1953 IN VEN'TOR.'

MW MMM ATTORNEYS.

United States Patent O LIQUID-COOLED GASEOUS-DISCHARGE TUBE John H. IIutchings, Geneva, Ill., assigner to National Electronics, Inc., Geneva,Ill., a corporation of Illinois Application July 30, 1953, Serial N o.371,361

1 Claim. (Cl. 257-2) The invention relates to liquid-cooledgaseous-discharge tubes;` it is particularly directed t agaseous-discharge tube having design characteristics which permit it tobe made primarily from inexpensive materials and at the same time topossess excellent performance characteristics.

The present invention is applicable to an extensive class ofgaseous-discharge tubes, including particularly mercury-vapor tubes usedas rectiers, circuit interrupters, and other applications whereincurrents of large magnitude are involved. In all such applications, tubecooling is an important design consideration. In many instances, thequantity of heat to be dissipated by a given tube in normal operation isso great in proportion to its size as virtually to compel the use ofliquid cooling. The liquid employed as coolant is in nearly all caseswater, which makes an admirable liquid for the purpose, because of itsnegligible cost and high specific heat.

This situation has led to extensive prior-art development effort in thefield of Water-cooled discharge tubes. Various types of successfulwater-cooled tubes have been developed in the past, and it isaccordingly understood that the present invention does not purportbroadly to cover that field. The present invention relates, on thecontrary,

2,756,027 Patented July 24, 1956 ICC perhaps, than a thermostaticelement responsive tothe temperature of the cooling water. In most casesno temperature control was even attempted. Protection was merely againstwater failure, a suitable shut-down means being provided to turn off thepower if water ow dropped below a predetermined level. Obviously such anarrangement, requiring full water flow regardless of the load on thetube, is extremely wasteful of water and hence uneconomical. Another'important object of the present invention is to provide a water-cooledgaseous-discharge tube wherein means are provided for virtuallyinstantaneous measurement of tube temperature, permitting much moreprecise control of tube temperature than was possible with prior-arttubes and, in consequence, permitting co-ntrol of the rate of waterflow.

In the accompanying drawing, I have described a typical embodiment of myinvention, consisting of a socalled ignitron tube, which is amercury-vapor tube useful as a rectifier and also as a high-currentswitch.

In the drawing, Figure l is a perspective View in elev vation of a tubemade in accordance with the present into a particular design ofliquid-cooled discharge tube f whose performance is superior to that ofearlier types and which has the advantage that it can be made with lessexpensive materials than required in prior-art types.

In the detailed specification of the invention which follows, I shallmake frequent reference to water as a cooling medium, but it will beunderstood that water is being thus employed only as an illustrativematerial, and that the structure described can, if desired, be used withother cooling liquids.

Prior-art water-cooled gaseous-discharge tubes have in general been madewith a metallic housing, glass being used only for the necessary sealspermitting maintenance Within the tube of a low gas pressure whileproviding a means for making external connections to the internalelectrodes of the tube, such as the anode and the ignitor. The use ofsuch metallic jackets in conjunction with Water cooling, however, has inthe prior-art tubes required that the housings be made of expensivemetal, usually columbiumstabilized stainless steel. Use of cheaper ironor ordinary steel in prior-art designs has led to diiculty with rustingand loss of vacuum due to hydrogen leakage through the metal wall. It isa principal object of the present invention to provide a water-cooledgaseous-discharge tube which can be constructed of ordinary sheet ironor mild steel without vany deleterious effects on tube life oroperation.

Another serious problem with prior-art Water-cooled tubes wastemperature control. On the one hand, it is always imperative that thepower be removed from the tube the instant its temperature exceeds asafe value, but, on the other hand, shut-downs because of transientover-heating are expensive and are to be avoided except when tube safetyrequires them. Prior-art tubes, generally speaking, had notemperature-control means other,

vention. Fig. 2 is a vertical sectional view of the tube of Fig. 1, thesection being chosen to bring out the details of its internalconstruction. Fig. 3 is a sectional view in the horizontal plane, takenalong the line 3 3 of Fig. 2.

The ignitron tube shown in the drawing has a cylindrical metal housing10 and a coaxially disposed outer jacket 11. Housing l0 may be made ofwelded or seamless steel tubing, and jacket 11 may be made of sheetiron, suitably formed. Jacket 11 may if desired be suitably plated toprotect its outer surface and to give it a dressy, finished appearance.Near the top and bottom of the cylindrical housing 10 metal end plates11a and 12 are inserted and welded thereto. To insure the existence of agas-tight seal between the end plates and the housing, the end platesare provided with annular anges 11b and 12a, which are preferablyseam-welded to casing member 10 around the entire periphery of the endplates. the respective ends of housing 10 and jacket 11, thus closingoff the annular space between the housing 10 and the jacket 11.

A spirally disposed coil of tubing 15 is Wrapped aro-und and brazed tothe housing 10, the coil being made of copper or other suitablerust-resistant and heat-conducting metal and terminating at therespective ends of the tube in inlet terminal 16 and outlet terminal 17.The coil thus formed by tubing 15 is a cooling coil through which wateror other cooling liquid will be circulated during tube operation. l

The coil formed by tubing 15 will normally, be wound with greaterdensity near thesbot'tom portion of housing 10, since it is in that zonethat the mercury condenses, and maintenance of relatively cool walls inthat region is therefore of paramount importance. Brazed to the outersurface of tubing 15, and covering suiiicient area to embrace one ormore turns of the cooling coil, is a disc or plate 18 preferably made ofcopper. Overlying disc 18 jacket 11 contains an aperture 19, providingaccess from outside the tube to the outer surface of disc 18. Disc 1S isnot brazed to jacket 11, and may preferably be insulated from jacket 11by a very thin layer of the hightemperature sealing compound to bedescribed. The shape of element 18, it will be understood, is a matterof choice; rather than being formed as a disc, it may be rectangular orany other desired shape. While I have shown the upper surface of disc orplate 18 recessed slightly below the outer surface of jacket 11, theplate may, if desired, be made of suliicient thickness to be ush with,or to extend outwardly beyond, the surface of jacket 11.

Similarly, annular caps 13 and 14 are iitted over' The entire'space-between housing 10 and jacket 11, apart from the` space Yoccupiedby the tubing and the disc 18, is filled with artificial rubber or otherhigh-temperature sealing compound 20. This material is placed in `theannular Space `between `housing 110 tand ,ijacket 11 whenfn a;plasticycondition, and isintroducedin any suitable manner to insure that it llsthetentirespace available to'it. This materiabprovidescompleteinsulation of the tubing l15 and the housing `10 against contact`with air. It Awillbe understood-thatannular caps :13 and 14 thusfunction asmechanical closuresonly, the sealing function being:entrusted to compound 20.

The components `of the `tube'inside `the housing 19may beconventional.`In the` device illustrated in the drawing, Ihave -shown thelowenportion of the tube interioreccupiedbyia `pooliof liquid mercurytl,ywhich may fill thetube to a depth of-perhaps one-`fourth inch. Suitablyweldeduinto apertures in bottom plate 11a, are an evacuation tube 26aand `a glass seal-member 22 for supporting theiignitor lelectrode .andproviding a means for making externalncontact thereto. Passing through,glass yseal 22 is afrelativelyrigid conductor 23 extending into thespace abovethernercurypool 21. The upper end of conductor 23 carriesa'transversel metallic support member 24 which is `crimped at its freeend around a .carbon electrode 25. Theflowerend of electrode 2S, whichis `generallypenclshaped, isgprovided with a tip -26 made ofiboron`carbide or `other lmaterial of intermediate conductivity. .Tip 26extendsdownward into mercury pool 21. A lead 27 may be provided ifdesired to insure good electrical contact between support `member 24 and`electrode 25.

Thestructure just describedis commonly known in the art as an ignitor,the particular discharge tube described in the present specificationbeing of the type commonly called .ignitron.

The 4upper portion of `the tube is provided `with an anode28,;preferably made ofv graphite, which is insulatedly-supported on topplate'12 by means of an annular glass seal 29. Ailexible lead 31 extendsoutward and `upward from seal =29'to.provide aconvenient externalconnection to anode28.

Extension 32 ,provides asimilar external contact element .for making`electrical connection to the .mercury pool 21, `which functionselectrically ascathode.

Operation In the operation of my invention, cooling water may be pumpedthrough tubing 15,at a rate determined by the` load ontheitube and theinitial temperature of-the water. In anycase, the heatgenerated in thetube operation may in that mannerbe carried awaypromptly, the tubetemperature beingheld at a safe value at all times. A .thermostat may bemounted in .contact with plate 18, which, `by reasoniof `being brazed totubing 15, provides a reliable measure of the housing temperature at alltimes. (Since the tubing 15 is highly heat-conductive and is`itselfjbrazedto housing 10, the.temperature.of plate '18 `at all times closelyapproximates the actual temperature of housing 10.) The ,externalcircuit controlled by the thermostat may be connected in conventionalfashion to control the ow of water to maintain the tube at optimumoperating temperature, and, of course, may be arranged to turn off thepower in the event the temperature, for any reason, exceeds a safevalue.

In operation, no air ever reaches either tube 15 or the surface ofhousing 10 adjacent tube .15, due to the protective action of the fillermaterial `20. As a result, no condensation of moistureever-takes placeonthesurface of housing `10, and `no problem of hydrogen leakage throughthe walls of housing 10 exists even when housing 10 is made ofinexpensive sheet iron.

It s accordinglypossible by means of the structure herein disclosed, toprovide a long-lived, Water-cooled discharge tube, at a manufacturingcost substantially below that required for prior-art Water-cooled tubes,which has .great advantagesoverprior-art tubes, particularly in respectto economical use of cooling water.

It will be understood that numerous changes andmodifcations in thedisclosed structure may be'made bypersons` skilled in the art withoutdeparting from the spirit of my invention. Itis accordingly my desirethat the foregoing description be regarded `asillustrative only, andthat the Vscope of my inventionybe determined primarily withreference tothe appended claim.

lclaim:

-iFor-use with a sourceof cooling liquid and .thermostaticallycontrolledmeans for regulatingthe ow :thereof,.a gaseous-discharge device adaptedlto be cooled by circulation of liquidycomprisinga metal'housing, anelongated `metal, liquid-tight tube `spirally surrounding said housingand bonded thereto along a substantial portion of its length, said tubehaving inlet and outlet ends adapted for connection to said source, anouter jacket surrounding said housing and said tube, providing`therebetween an enclosed space, means 4withinsaid `enclosed spaceetfectively sealing off fromaccess to air the outer surfacesfofsaidhousing and of `theportion .of said tube in intimate contact withsaid housing, said sealing means being .operative to provide at leastpartial thermal insulation for said housing andsaid tube, `and meansadapted for cooperation with said thermostatic `means comprising a metalplate bonded to said tube on the surface thereofopposite said housing,said plate being substantially heat-insulated from said jacket, theportion of saidjacket adjacent said plate beingiat least `partiallyrelieved to permit contact between said plate and saidrthermostaticmeans.

References Cited in the le of this patent UNITED STATES EPA-TENTS2,121,579 Bahls June 2l, `1938 '2,275,852 Herskirld Mar. 10, 19422,313,379 Wood Mar. `9, y1943 2,595,150 Lemeshka Apr.'29, 1952

